MCP servers, skills, CLIs, and tool contracts are all attempts to solve the same problem: how does an agent use software without pretending to be a person clicking around?

The important part is not the acronym. The important part is the contract.

A good tool contract tells the agent what jobs are available, what inputs are required, what outputs mean, what errors are possible, what permissions apply, and what side effects may happen. It should be stable enough that workflows can be built on it. It should be descriptive enough that the agent does not need a tribal-knowledge paragraph in every prompt.

MCP is promising because it gives teams a common way to expose tools and context to agents. Skills are useful because they package local instructions, conventions, and workflows around those tools. CLIs are powerful because they make operations scriptable, inspectable, and easy to run outside the product UI. None of these are magic. A sloppy MCP server is still sloppy. A skill wrapped around a bad tool is still a workaround. A CLI with confusing flags is still a tax.

The product discipline is deciding what contract you want autonomous workers to rely on.

That means naming matters. Schemas matter. Examples matter. Rate limits matter. Idempotency matters. Error messages matter. Versioning matters. So does documentation that explains the business meaning of actions, not only the parameter list.

A contract should also reflect the product's real operating model. If the safest way to update a renewal plan requires checking account tier, open escalations, owner approval, current contract terms, and customer communication history, do not expose a bare “update renewal plan” mutation and call it done. Encode the guardrails. Offer a dry run. Return the reasons.

The best agent-native products will feel like they have an operations manual built into the interface. The agent can discover what is possible, choose the right command, verify the plan, and recover when something fails.

This is the layer where product design and developer experience merge. The user is an agent, but the buyer is still a human trying to get work done safely.

Tool contracts are how that trust becomes executable.

This is part 9 of 10 in Agent-Native Tools.